Optimization of Plasma Treatment, Manipulative Variables and Coating Composition for the Controlled Filling and Coating of a Microstructured Reservoir Stent

Abstract

The object of the study was to fill and coat the microcavities of a drug eluting stent using a batch dipping process. 316L coronary stents, which were coated with a 0.25 μm layer of TiNOx were used as substrates. The stents’ surface was dimpled with 0.21 μl microcavities separated by distances of 17–28 μm depending on location. The experiment consisted of (1) optimizing the procedures to fill the microcavities with a solution of therapeutic agent and (2) covering the filled microcavities with a protective “lid” that shielded the solution during stent insertion in the arteries and then controlled its release into the surrounding tissue. The filling solution was a water-propanol mix containing 20% L-arginine. The coating solution was comprised of poly-ethylene-glycol (PEG-8000) and dexamethasone. The filling quality was investigated after altering the following variables: plasma surface activation (type of gas, pressure, power, and duration), water-propanol percentage ratio of the filling solution, lifting speed from the bath, and effect of ultrasonic vibration (monofrequency versus multifrequency). The surface coating was evaluated by altering the PEG-8000-dexamethasone percentage ratio and recording the effects on coating thickness and structure, on elution rate, and on wear resistance. The optimized process is presented in detail.